Synthesis and properties of imidazolium-based ionic liquids

Six kinds of ionic liquids 1-alkyl-3-methylimidazolium bromides were synthesized from N-methylimidazolium and alkyl bromides with microwave irradiation.The ionic liquids investigated here were 1-n-propyl-3-methylimidazolium bromide,and 1-iso-propyl-3-methylimidazolium bromide,1-n-butyl-3-methylimidazolium bromide,1-sec-butyl-3-methylimidazolium bromide,1-n-amyl-3-methylimidazolium bromide,and 1-n-hexyl-3-methylimidazolium bromide.1-n-butyl-3-methylimidazolium bromide was converted into 1-n-butyl-3-methylimidazolium tetrafluoroborate after anionic exchanging.Density of ionic liquids was measured at 25 ℃.The results showed that density of ionic liquids with same anion decreased as the length of the alkyl chain on the cation increased.For a given cation,the density increased as the volume of the anion increased.Cyclic voltammograms study revealed that the potential windows of 1-n-butyl-3-methylimidazolium bromide and 1-n-butyl-3-methylimidazolium tetrafluoroborate were 2.0 V and 3.4 V,respectively.DSC curve of 1-n-butyl-3-methylimidazolium tetrafluoroborate showed that it had glass-transition temperature(-95 ℃) and had not crystallization and melting temperatures.